I've been making Challah for close to 50 years, and I'm not sure what else you would use! I am particular about using organic flour, but unbleached, all purpose is all I've ever used -- with great success, I might add. ;)

How fascinating, Cynthia! I come from a mixed family, but none of my Gentile relatives have ever made or even eaten Challah unless they visited us. And I've never heard of it as an Easter Bread. Jews eat it year around, except at Passover when flour and yeast are not allowed. And unless it's to be specifically for a Dairy meal neither milk nor butter is included. When I put milk and butter in my Challah recipe, it becomes Brioche!

Challah itself is not an Easter bread; rather, the word "challah" is a biblical Hebrew term denoting the double loaves of bread over which a blessing is recited at the Sabbath meal. They represent the double portion of mannah that was provided for the children of Israel during the Sabbath; it also refers to the soft, egg-based, often braided loaf typically used for that purpose (although other versions, such as water challah, a white loaf, are popular as well). Although there are sweet eggy breads in other cultures, challah is traditionally dairy-free to permit its inclusion in meat meals, since the combination of meat and dairy is not allowed.

I would definitely use mostly, all-purpose flour (or bread flour) in a recipe for a free-form bread. I find using exclusively whole wheat flours can be tricky with bread since the bran can interfere with gluten development. Since challah is enriched, which further inhibits gluten, I would suggest using all-purpose (especially since you want strength but softness). If I'm experimenting with alternative flours, I will start with ¼ substitutions and increase/decrease from there.